The present invention relates to new compositions which are suitable for the manufacture of lamp reflectors. More particularly, the invention relates to new unsaturated polyester resin compositions which are adapted for the manufacture of lamp reflectors for spotlights, fog lamps or moveable headlamps of motor vehicles.
It is known to manufacture bodies in the shape of a dish of a lamp reflector by polymerizing a moldable unsaturated polyester resin composition containing an antishrinkage agent, glass fibers, fillers and a demolding agent. The known antishrinkage agents employed hitherto in the case of the manufacture of lamp reflectors consist most frequently of polyvinyl alcohol, polyurethane, and more rarely of polyethylene or polystyrene. Where demolding agents are concerned, zinc stearate or calcium, lithium, barium or magnesium stearate and the like have most frequently been proposed hitherto.
The present inventors have found that the antishrinkage agents employed hitherto do not make it possible to obtain reflectors having a surface which remains sufficiently perfect with time to maintain high shape integrity and superior optical properties. Where these properties are concerned, the inventors have found that the use of the demolding agents employed hitherto resulted in fogging on the reflecting surface because of the evaporation of the demolding agent which then condensed on the reflecting surface at the elevated temperatures which are encountered while the reflector is in use. Such elevated temperatures result from the use of high-intensity bulbs as a light source and because of the reduction in the volume of reflector parabolas related both to recent changes in aerodynamic and aesthetic factors in reflector lamps. This evaporation of the demolding agent is observed as a loss in the weight of the reflector.
It can be seen that there is therefore a need to develop reflectors which exhibit a minimum loss in weight when heated and which thus retain irreproachable and superior optical properties over time.